As noted above, the invention pertains generally to clutches and brakes. For the sake of brevity the invention will be described in terms of electric clutches and brakes, but the invention could be used in conjunction with other types of clutches and brakes.
As well known to those skilled in the art, electric clutches and brakes typically include an input member, an output member and a casing or housing which contains electromagnetic components suitable for selectively coupling the input and output members. In the case of an electric clutch, the housing or casing contains electromagnetic components suitable for selectively coupling the input and output members (e.g., axially-aligned shafts) to cause them to rotate together. By contrast, the housing of a brake contains electromagnetic components suitable for selectively coupling the input member (typically a shaft) to the output member which is rigidly connected to the housing which in turn is rigidly connected to a stationary point. In addition to electric clutches and brakes, there are combination clutches/brakes which can either selectively couple a pair of shafts or apply a braking torque to an input shaft.
In all cases, i.e., clutches, brakes, and combination brakes/clutches, there is a need to secure the housing or casing of the torque applying device against rotation. For all three types of devices, there are wires running from an electrical power source to the electromagnetic components within the housing. Unless slip rings or the like are used, the housing or casing of a clutch or brake/clutch must be secured against rotation to prevent the wires from wrapping around the rotating members. Also, it is obviously necessary to secure the housing of a brake against rotation so that braking torque can be applied to the rotating input member to reduce its speed.
While the present invention could be applied to a wide variety of electric clutches, brakes, and brakes/clutches, for the sake of brevity the remainder of this discussion and the detailed description of the invention will focus on combination brakes/clutches. Such devices are used between the prime mover and mower blade of large commercial turf mowers. When it is desired to cut grass, the clutch is activated to couple the prime mover to the mower blade. The clutch is de-energized to stop the blade.
Securing a brake/clutch housing against rotation has been a long-standing problem. Historically, simple threaded connectors or the like were used to fasten the brake/clutch housing or lever arm extending therefrom to a nearby stationary member. While this might seem to be a simple solution to the problem, it has been discovered that this connection scheme is fraught with many problems of its own. For example, the threaded connector (or the like) can loosen over an extended period of time and become the source of bothersome noise and vibration. Furthermore, the connector between the brake/clutch housing (or housing lever arm) and the stationary member can fatigue and break. When this happens, the brake/clutch becomes nonfunctional, potentially leading to a dangerous situation in the event braking is immediately needed.
The loosening and fatiguing problems discussed above are thought to be primarily attributable to two sources: (i) torque induced on the housing (and/or housing lever arm) during normal operation of the device; and (ii) forces caused by "runout." Runout is defined herein as any radial motion of the housing. Runout can be caused by an eccentric or loose input shaft, or a poorly constructed brake/clutch. Runout can result in a sizable amount of stress at the connection point between the housing (or lever arm extending therefrom) of the brake/clutch and the stationary member. If runout is eliminated by very rigidly clamping the brake/clutch housing to a stationary member, this can cause undue stress on the internal mechanism of the brake/clutch. On the other hand, if the traditional housing securing technique is used (i.e., simple threaded connector or the like), and runout is permitted to some degree, a destructive sawing action can result between adjoining parts.
The present invention addresses the problems associated with securing a brake/clutch housing to a stationary member. In particular, the invention is directed toward accommodating "runout" while preventing the housing connector from breaking due to fatigue, "sawing action" or the like.